Orthotrichum Moss (Orthotrichum tenellum)
Description
Orthotrichum tenellum, Tufts of O. tenellum are composed of several narrow, upright shoots with appressed leaves, topped by narrow capsules almost completely hidden by a long, sparsely hairy, light green calyptra. The plants are consistently less than 1 cm tall and are often less than 5 mm in height, with leaves 2.5-3 mm long and capsules 2 mm long. Unripe capsules are light green; when ripe or old they become golden brown, and have 8 reflexed, orange outer peristome teeth. Small plants of O. affine (p. 647) can be confused with relatively tall O. tenellum, and checking the stomata with a microscope is often necessary. The narrowness of every feature of O. tenellum is distinctive, as is the long calyptra, which almost hides the capsule, whereas the calyptra of O. affine and most other species ends well above the base of the capsule. The very rare O. pumilum (Smith, p. 677) has shorter calyptrae, and forms tiny (less than 4 mm), squat tufts in contrast to the slightly taller, narrow tufts of O. tenellum; it undoubtedly needs checking with a microscope. O. tenellum is the commonest Orthotrichum on trees and shrubs in the Mediterranean, and in Britain is most at home in the south-west. In some coastal areas, it is abundant on elm (Ulmus) trunks and willow (Salix) branches, as well as a variety of street trees. Further north and east, it occurs in small quantity on ash trees (Fraxinus excelsior) in parkland, or on old elders (Sambucus nigra) in hedgerows. Atmospheric pollution caused it to disappear from much of lowland England, but it is now slowly spreading back into the Midlands.
Taxonomic tree
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Domain: Eukarya
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Kingdom: Plantae
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Phylum: Bryophyta
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Class: Bryopsida
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Order: Orthotrichales
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Family: Orthotrichaceae
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Genus: Orthotrichum
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